Transmission control



Jan. 1, 1935. s. B. WRIGHT ET AL TRANSMISSION CONTROL Filed Aug. 29,1951 Pmportzbl zal Dear/waging Circuit M'Pindz'catespolizg qf batteriesINVENTORS 61B. Mite/Laid ATTORNEY Patented Jan. 1, 1935 flssaiiz, f, v

TRANSMISSION co 'raoL l t, South f jii giants pas Mitchell,Martinsville, N. J., assignorsjto Ameri can Telephone and TelegraphCompany, a; cor- I notation of New York Al p icationAugnstfill, 1931,Serial: N te-@216 I y :]c1ai111 1 s. (01479-170) 'I'his'inventionrelates to systems for' the transmission of energy. More particularly,the invention relates to telephone systems, over which are transmittedthe electrical waves repthe invention relates. to telephonecircuitsespecially four-wire circuits-4n which transmissioniscontrolled'by switching devices responsive to energy in the transmissionpaths.

In'a telephoneicircuit it is often desirable to maintain l a normal, ornon-operating, condition of disability; in order to prevent singing. IIt then becomes necessary, of course; to causesthe removal of thisdisability when speech energyis transmitted. In thecase of alfour wirecircuit, in which the path normally disabled is associated with a" pathfor transmission inthe oppooperation of the transmission controlapparatus.

It is feasible. to employ ,manually operated controls'for adjusting thelosses in thetransmission paths and the sensitivities of the wavesresponsive transmission, control apparatus, with a view to reducing thechance of false operation of that apparatus, and suchadjustment is.usually'desirable. It is important, however, especially, in the case ofa system including ,anoisy or otherwise mutable. link, thatfurtherprecautions'be taken against undesired operation of transmissioncontrols byinterfering energy, and

it is likewise important that such precautions do not involveunnecessary lowering-of-volume in the transmission paths. ,j N1; r, Itisproposed to disclosethe applicants in- I ventionas applied to theterminal of 1 a four- -wire circuit having ,a transmitting? path adaptedto transmit energy, such as that representing speech, -from ;a;-two-wire circuit to a 1 noisy link, such as aradio 1ink,--and afreceiving path adapted for the transmission, of energy from the noisylink to the two-wire circuit, t I

One of theprincipal objects of the invention .L at the left to a noisy,link (indicated), at ,the right. The one-waytwo-wire path, L1. isadapted for transmissionfrom circuit L to the noisy link, and theone-way path L2 is adapted for trans- ,solved-by the applicants. i i y ia Inthe oneway-path L1 a vacuum tube T1 with associated elements tobediscussed hereinafter, ,(oran equivalent device) provides avariableimpedallwcghridged across the transmission line. ,2

is the automatic adjustment of the sensitivity of the transmissioncontrol apparatus responsiveto energy in the "receiving path inaccordance with the'incomingstatic or other interfering energy.

- Another object'of the inventionis the automatic adjustmentof thereceiving volume in accordance with theincoming statici It will beunderstood that the accomplishment of theuabove-stated objects has theultimate result of rendering more nearly satisfactory the operation ofthe wave-responsive transmission controls, including 'the' singi'ngsuppressor" control, without avoidable reduction of the volume deliveredto the subscriber connected -to' the two-wiricircuit; for instance; iThe applicants, in general; utilize 'afidesensitizing? :circuit, and .bya novel arrangement of circuit.elements provide for:the 'adjustnient 'ofthe ,receiving, transmission control. apparatus sensitivity or theadjustment of the.receiving volume, or both, in accordance "witht the"static orother interfering energy in thereceiving path.

The arrangement is such: that substantiallyno unnecessary reduction ofreceived volume 'is introduced.

The invention will be clearlyunderstood when the following descriptionof one desirable embodiment and the operation thereof is read withreference to the accompanying drawing, showing the; circuitsindiagrammatic and partly in schemati orm-m 1, L i w With -reference to ithe details of the drawing, there. is ,disclosedthe left-hand terminalof a four-wire, circuit connecting a two-wire circuit mission from thenoisy link to the circuit L.

The connection between the two-wire circuit L and the four-wirecircuitis made through the ,hybrid coil HC, associated with anartificialnetwork the impedance of; which simulates rather .poorly theimpedanceof the line L. It will be understand thatthe link indicated aslyingto the right of thefour-wire circuit may be any mutable linkinwhich the occurrence of intersk ing-energy is likely. f Itfwill bewell, however,

tothinkpf this ,mutable link as a radio clink, in which static givesriseto one of the. problems Likewise, the vacuum tube T2 with its associatedelements (or the equivalent) provides a variable impedance connectedacross the one-way transmission path L2.

It will be noted that the path L1 is normally the point e by theoperation of a relay ES;

which may be termed the echo. suppressor relay.

The operation of relays SS'andES indirectly controlled by theamplifier-detector v.ADi' assb-j ciated with the path L1 at point b. Itshould be noted further that anamplifier-detector AD2 hereinafter.

' 'Iheregularor normal control ofvolume in the transmission paths L1 andL2 is specifically disclosed as involving the manual operation ofpotentiometers :P1 and P2, tied together for simultaneous. operation asindicated in the drawing., It should be noted at this point that theamplifier-detector AD1 responds to energy in path L1 at point hand thatamplifier-detector AD2 responds to energy in path L2 a'point d.

Let it bexassumed that a talker of weak voice is connected to'the lineL; Since the path L1, over which the voice waves are to travel, is underthe normal.'disability at point a, it now becomes necessary to removethis disability by the operation of relayaSSJ It is also desirable thatthe op'posite path L2 be "disabled at point a for the-suppressionofiechoes by the operation of relayxES. It will'be noted that whenamplifier detector1AD1 operates, a relay S, having its wind- "ingfincluded in the outputcircuit of the amplifier-detectoroperates toconnect battery to the windingsxofr-relays es and ES and thus to causethe operationsof these two relays. Accordingly, in the 1 caseiof i aweak talker connected to the line L, it may be necessary to decrease theloss :introduced in path L1 by the apparatus including the vacuumitubeT1; For this purpose-the po- ..tentiometer 'arms are turned in aclockwise direction. operation of the potentiometer P1 increases; thenormally considerable negative biasing voltage impressed onthe grid oftube T1 and" raises i the tube impedance b'ridged' across the path-L1.Thisoperation, of course, results m decreasingthe'loss introduced in thepath'L1,

and this-adjustment permits the response of amplifierdetectonAD and theassociated relays to the comparatively weak voice energy applied. --The'path L1 is now'clear at posite'p'ath' L2 is blocked'atpoint c. '60

. i'togeth'er, the operation of the devices not only point a, and theop- Since the'two potentiometer arms are tied adjusts the setting ofpotentiometer P1 to change the lossin path L1 but also adjusts thesetting of potentiometer P2, When the arm of potentiometer P2 is turnedin a clockwise direction,'the

normally excessive negative bias impressed on --the"gr'id of tube' -T2from battery B2 is reduced. -By "the time that-"the loss in path L1 issufiiciently lowered to give-"the likelihoodof false originating in pathL2 which is too weak to operate relay S 'and is reflected back over pathL1 from the two-wire circuit L, the impedance of 7 tube-T bridged acrossthe path L2 is appreciably 5 v operation of amplifier-detector AD byenergy lowered-and increased loss is introduced into the receiving path.This operation, it will be understood, prevents false operation ofamplifier-detector AD1 by reflected energy.

It will be noted that filter F1 is interposed between the potentiometerP1 and tube T1 and that a filter F2 in interposed between potentiometerP2 and the tube.,'I2. These. filters serve to prevent clicks in thetelephones connected to the transmission lines, as a result ofsuddenchanges .in the settings of the potentiometers.

It will be noted that a polar relay S, with 'two1., windings, has itsright-hand winding 101 connected in the output circuit ofamplifier-detector AD2 andthat this winding is arranged to attract therelay armature to its front contactand thus open-the output circuit ofamplifier-detector ADn The left-hand winding of is connected across theline L2 .at point at andcontrols switching apparatus to be; discussedthis relay- 102 is arranged to exert a force in opposition to windingan, that is, to hold the armature of relay S on its back contact andthus to maintain the closed condition of the output circuit ofamplifier-detector AD1. When. ener-. gy comes in over thepath L2 andpasses the point 0, it normally causes the operation ofamplifier-detector AD2,-which in turn causes the operation of relay. Sand opens the output circuit ofamplifier-detector AD1. This operationprevents the operation'of relay S, and conse-. quently the operation ofrelays SS and ES, in response to later arriving energy in path L1. Itwill be understood, however, that-without further provision this relayS. is subject to undesired operation by noise or other interferingenergyin path L2 as well-as to the desired operation by voice energy in thispath.

It .will be understood, further, that noise en ergy coming in over thepath L2 may reach path .L1 by freflection from circuit L and'may causefalse operation of the amplifier-detector AD1 and the relays controlledthereby. i For thepurpose of preventing the above suggested undesirableoperations, the applicants employ a proportional desensitizingcircuittogether with other apparatus now totbe'discussed.

The proportional desensitizing circuit com.- prises vacuum tubes T3, T4,T5, T6 and T6 and various resistances and capacities. The principle. of.this circuit. and theoperation thereof .areclearly disclosed and fullydiscussed in UnitedStates Patent No; 1,772,551 to Mitchell and Silent,and accordingly a detailed description or discussion herein isunnecessary." It is effect in response to the energy of comparativelysustained level. This efiect is the variation of the plate current inthe tubes T6 and Te (which are connected in parallel) in accordancewith" and in proportion to the energy of sustained level.

It will be noted that the windingw2 of relay S is connected in theplate' circuit'of the vacuum tube T6 of the desen'sitizing-circuit. Thuswhen noise energy, or the like, comes in over the path L2, a bias isgradually built up through energization of winding w2, and this bias issufficient to prevent the 'operation of relay S due to energization ofwinding 101 connected in other words, the relay S" isdesensitizedinacoordance with the noise energy or other energy of sustained levelto'the pointfwhich prevents its operation bynoise or the likefand theconenergymay havepassed point d in path Lz without operating relay S"and ,in itsfreflected form may operate amplifier-detector "AD1. y With;this difficulty in their minds, the applicants provide" for auxiliaryadjustmentjflof the loss introduced in path L2 by tube ,T It willbeinoted'thata resistance R is included in the plate circuit of tube T6 ofthe desensitizing device. lihis lre- ,sis tancemaybevariable to give asuitablei'ni tial adjustment.

As the energy of sustained level causes" the operation ofthedesensitizing circuit, a voltage is built up across the resistance:R'(or the effective;portionflof this resistance) which tends'tocancel'thenegative voltage applied to the grid of tube T2 bythe batteryB2. This auxiliary voltage reduces the impedance of the tube T2 andincreases or tends to increase the loss introduced in path L2. vThus, ifthe potentiometer arms are turned in a clockwise direction to adjust fora weak talker, the volume While the invention has been disclosed specifically for the purpose of illustration, it is to be understood thatsuch disclosure does not limit the scope of the invention, which isdetermined by the appended claims.

What is claimed is: I 1. In a system for the transmission ofenergy,

a transmission path, control means in said, path, for introducing avariable loss. therein, and

means responsive to energy of comparatively sustained level such asnoise in said path, which energy may be in a frequency range includingthe voice range, for adjusting said control means to vary the lossintroduced thereby in said path, said last-stated means beingsubstantially unresponsive to energy of rapidly fluctuating level suchas speech.

2. In a system for the transmission of energy,

a transmission path, control means in said path for introducing avariable loss therein, and means responsive to energy of comparativelysustained level such as noise in said path, which energy may be in afrequency range including the voice range, for adjusting said controlmeans to vary the loss introduced thereby in said path in proportion tothe magnitude of said energy, said last-stated means being substantiallyunresponsive to energy of rapidly fluctuating level such as speech.

r 3. In a system for the transmission of energy, two paths adapted fortransmission in opposite directions, means for normally disabling thefirst path, clearing means responsive to energy in said first path forremoving the normal disability therefrom, control means normallyresponsive to energy in the second path for preventingthe removal ofsaid disability on said first path, and means responsive substantiallyonlyto energy of comparatively sustainedlevel in said I second path fordesensitizing said control means. Ina system for the transmissionofenergy;

two paths adapted for transmission in opposite directions, means fornormally disabling the first path, transmission control means responsiveto energy in said first path for removing the nor mal disabilitytherefrom and disabling the sec-- ond pathflcontrol means normallyresponsive to energy'in said second path for preventing the operationvof said transmission control means, and means responsive substantiallyonly to energy of comparatively sustained level in said second path fordesensitizing said later named control means.

5. In a system for the transmission of energy,

two paths adapted for transmission in opposite directions, gain controlmeans in each path for introducing a variableloss therein, meansfornormally disabling the first path, clearing means responsive to energyin said first path for removing the normal disability therefrom, controlmeans responsive to energy in the second path for preventing the removalof said disability on said first path, and means responsivesubstantially only to energy of comparatively sustained level in saidsecond path for desensitizing said control means and. for adjusting theoperation of the gain control means in said second path.

6. In a system for the transmission of energy, two paths adapted fortransmission in opposite directions, gain control means in each path forintroducing a variable loss therein, means for adjusting thesetting ofsaid gain control means, means for normally disabling the first path,transmission control means responsive to energy in said first path forremoving the normal disability therefrom and for disabling the secondpath, controlmeans normally responsive to energy in said second path forpreventing the operation of said transmission control means, and meansresponsive substantially only to energy of comparatively sustained levelin said second path for desensitizing said last-named control means andfor introducing anauxiliary adjust- 'ment of the setting of the gaincontrol means in said second path. e i

7. In a system for the transmission of energy, a four-wire circuitincluding a first path adapted to transmit energy to a mutable link ofthe system and a second path adapted to receive energy from the mutablelink, means for normally disabling said first path, clearing meansresponsive to energy in said first path for removing the normaldisability therefrom, and control means associated with said second pathfor preventing the operation of said clearing means, said control meansbeing responsive to the energy in said second path which is transmittedover the system for the production of the desired over-all eifect butunresponsive to interfering energy received in said second path from themutable link.

8. In a system for the transmission of energy, a four-wire circuitincluding a first path adapted to transmit energy to a mutable link ofthe system and a second path adapted to receive energy from the mutablelink, means for normally disabling said first path, transmission controlmeans responsive to energy in said first path for removing the normaldisability therefrom and for disabling said second path, and controlmeans associated with said second path for pre-,

trolwimeans, said control means being responsive to the energy inzsaidsecond path which is transmittedover the system for the production ofthe desired'over-all effect but unresponsive to interfering-energyreceived in said second path from the 1 mutable link. I asystem'forthetransmission of energy,

two paths adapted for transmission in opposite directions, the first ofsaid .paths being subject to the reflection thereover of energyrnormally transmitted over the second path, transmission controlapparatus responsive to energy in said first path, gain control means ineach of said pathsadapted for simultaneous adjustment, and means.responsive to energy of comparatively sustained level such as noise insaidsecond path for introducing an auxiliary adjustment of the I gaincontrol means in said second path Without changing the gain in saidfirst path, said noisesive to energy of rapidlyfiuctuating level such asv speech.

ventingtheoperation of said transmissioncon-i .10. Ina systemfor thetransmission of energy, a first transmission path adapted to transmitenergy to ,a mutable link of the system, and a second transmission path:adapted to receive energy from the mutable link, said first path beingsubject to the reflection thereover of energy normally transmitted oversaid second path, transmission control apparatus responsive to energy insaid first path, gain control means in each of said paths adapted forsimultaneous adjustment; and means responsive to-energy of comparativelysustained level such as noise transmitted over said second path from themutable link' for introducing an auxiliary adjustment of the gaincontrol means in said. second path without changing the, gain'inv saidfirst path, said noiseresponsivemeans being substantially unresponsiveto ,energy'of rapidly fluctuating level such as speech received in saidsecond path from the 20 mutable link. i e a SUMNER BISBEE WRIGHT.

- DOREN 1 MITCHELL. I

